A time-series plot showing the brightness of an astronomical object over time, designed to reveal exoplanet transit events as characteristic dips in flux. The plot displays photometric measurements with error bars against time or orbital phase, with an optional fitted transit model overlay. This visualization is fundamental in observational astronomy for detecting and characterizing planetary transits, variable stars, and other periodic brightness variations.
""" anyplot.ai
lightcurve-transit: Astronomical Light Curve
Library: matplotlib 3.11.0 | Python 3.13.14
Quality: 91/100 | Updated: 2026-06-20
"""
import os
import sys
# Prevent this file (matplotlib.py) from shadowing the matplotlib package
_d = os.path.dirname(os.path.abspath(__file__))
while _d in sys.path:
sys.path.remove(_d)
import matplotlib.pyplot as plt
import numpy as np
from matplotlib import patheffects
from matplotlib.patches import FancyArrowPatch
from matplotlib.ticker import FormatStrFormatter
# Theme tokens
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
# Imprint palette — position 1 for photometry, position 3 for transit model
BRAND = "#009E73" # Imprint position 1 — photometry data
MODEL_COLOR = "#4467A3" # Imprint position 3 — transit model curve
# Data
np.random.seed(42)
transit_center = 0.5
transit_duration = 0.08
transit_depth = 0.01
u1, u2 = 0.3, 0.1
half_dur = transit_duration / 2.0
n_points = 500
# Phase-folded observations
phase = np.sort(np.random.uniform(0.0, 1.0, n_points))
# Quadratic limb-darkened transit model for observations
model_flux = np.ones(n_points)
in_transit = np.abs(phase - transit_center) < half_dur
z = np.abs(phase[in_transit] - transit_center) / half_dur
limb = 1.0 - u1 * (1 - np.sqrt(1 - z**2)) - u2 * (1 - np.sqrt(1 - z**2)) ** 2
model_flux[in_transit] = 1.0 - transit_depth * limb
# Simulated photometry with realistic noise
flux_err = np.random.uniform(0.0008, 0.0020, n_points)
flux = model_flux + np.random.normal(0, 1, n_points) * flux_err
# Smooth model curve for overlay
phase_smooth = np.linspace(0.0, 1.0, 2000)
model_smooth = np.ones(2000)
in_transit_s = np.abs(phase_smooth - transit_center) < half_dur
z_s = np.abs(phase_smooth[in_transit_s] - transit_center) / half_dur
limb_s = 1.0 - u1 * (1 - np.sqrt(1 - z_s**2)) - u2 * (1 - np.sqrt(1 - z_s**2)) ** 2
model_smooth[in_transit_s] = 1.0 - transit_depth * limb_s
# Two-panel layout: full light curve + transit zoom (landscape 3200×1800)
fig, (ax, ax_zoom) = plt.subplots(
1, 2, figsize=(8, 4.5), dpi=400, facecolor=PAGE_BG, gridspec_kw={"width_ratios": [3, 1.2], "wspace": 0.15}
)
ax.set_facecolor(PAGE_BG)
ax_zoom.set_facecolor(PAGE_BG)
# === Main panel: full light curve ===
out_mask = ~in_transit
ax.errorbar(
phase[out_mask],
flux[out_mask],
yerr=flux_err[out_mask],
fmt="o",
markersize=2.5,
color=BRAND,
ecolor=BRAND,
elinewidth=0.7,
alpha=0.55,
markeredgecolor=PAGE_BG,
markeredgewidth=0.3,
capsize=0,
zorder=2,
label="Photometry",
)
ax.errorbar(
phase[in_transit],
flux[in_transit],
yerr=flux_err[in_transit],
fmt="o",
markersize=3.5,
color=BRAND,
ecolor=BRAND,
elinewidth=0.7,
alpha=0.9,
markeredgecolor=PAGE_BG,
markeredgewidth=0.3,
capsize=0,
zorder=4,
)
transit_mask_smooth = np.abs(phase_smooth - transit_center) < half_dur
ax.plot(phase_smooth, model_smooth, color=MODEL_COLOR, linewidth=1.8, zorder=5, label="Transit model")
ax.fill_between(
phase_smooth[transit_mask_smooth], 1.0, model_smooth[transit_mask_smooth], color=MODEL_COLOR, alpha=0.08, zorder=1
)
ax.axhline(y=1.0, color=INK_MUTED, linewidth=0.8, linestyle="--", alpha=0.5, zorder=1)
# Ingress/egress contact markers
t1 = transit_center - half_dur
t4 = transit_center + half_dur
for t_val, label in [(t1, "$t_1$"), (t4, "$t_4$")]:
ax.axvline(x=t_val, color=INK_MUTED, linewidth=0.6, linestyle=":", alpha=0.6, zorder=1)
ax.text(t_val, 1.0055, label, fontsize=9, color=INK_MUTED, ha="center", va="bottom")
ax.axvspan(transit_center - half_dur * 1.8, transit_center + half_dur * 1.8, color=BRAND, alpha=0.04, zorder=0)
ax.set_xlabel("Orbital Phase", fontsize=10, color=INK)
ax.set_ylabel("Relative Flux", fontsize=10, color=INK)
ax.tick_params(axis="both", labelsize=8, colors=INK_SOFT, length=0)
ax.spines["top"].set_visible(False)
ax.spines["right"].set_visible(False)
for s in ("left", "bottom"):
ax.spines[s].set_color(INK_SOFT)
ax.yaxis.grid(True, alpha=0.15, linewidth=0.6, color=INK)
ax.set_xlim(0.0, 1.0)
ax.xaxis.set_major_formatter(FormatStrFormatter("%.2f"))
leg = ax.legend(fontsize=8, frameon=True, loc="upper right")
if leg:
leg.get_frame().set_facecolor(ELEVATED_BG)
leg.get_frame().set_edgecolor(INK_SOFT)
plt.setp(leg.get_texts(), color=INK_SOFT)
# === Zoom panel: transit detail ===
ax_zoom.errorbar(
phase[in_transit],
flux[in_transit],
yerr=flux_err[in_transit],
fmt="o",
markersize=3.5,
color=BRAND,
ecolor=BRAND,
elinewidth=0.7,
alpha=0.9,
markeredgecolor=PAGE_BG,
markeredgewidth=0.3,
capsize=0,
zorder=4,
)
near_mask = (np.abs(phase - transit_center) < half_dur * 2.0) & ~in_transit
ax_zoom.errorbar(
phase[near_mask],
flux[near_mask],
yerr=flux_err[near_mask],
fmt="o",
markersize=2.5,
color=BRAND,
ecolor=BRAND,
elinewidth=0.7,
alpha=0.55,
markeredgecolor=PAGE_BG,
markeredgewidth=0.3,
capsize=0,
zorder=2,
)
zoom_phase = phase_smooth[transit_mask_smooth]
zoom_model = model_smooth[transit_mask_smooth]
ax_zoom.plot(zoom_phase, zoom_model, color=MODEL_COLOR, linewidth=1.8, zorder=5)
ax_zoom.fill_between(zoom_phase, 1.0, zoom_model, color=MODEL_COLOR, alpha=0.10, zorder=1)
ax_zoom.axhline(y=1.0, color=INK_MUTED, linewidth=0.8, linestyle="--", alpha=0.5)
# Transit depth annotation with double-headed arrow
min_model = zoom_model.min()
arrow = FancyArrowPatch(
(transit_center - half_dur * 1.6, 1.0),
(transit_center - half_dur * 1.6, min_model),
arrowstyle="<->",
color=MODEL_COLOR,
linewidth=1.2,
mutation_scale=8,
zorder=6,
)
ax_zoom.add_patch(arrow)
df_text = ax_zoom.text(
transit_center - half_dur * 1.5,
(1.0 + min_model) / 2,
f"$\\Delta F = {transit_depth * 100:.1f}\\%$",
fontsize=10,
color=MODEL_COLOR,
va="center",
ha="left",
fontweight="bold",
zorder=6,
)
df_text.set_path_effects([patheffects.withStroke(linewidth=3, foreground=PAGE_BG), patheffects.Normal()])
for t_val, label in [(t1, "$t_1$"), (t4, "$t_4$")]:
ax_zoom.axvline(x=t_val, color=INK_MUTED, linewidth=0.6, linestyle=":", alpha=0.6, zorder=1)
ax_zoom.text(t_val, 1.004, label, fontsize=9, color=INK_MUTED, ha="center", va="bottom")
zoom_margin = half_dur * 2.0
ax_zoom.set_xlim(transit_center - zoom_margin, transit_center + zoom_margin)
ax_zoom.set_ylim(min_model - 0.002, 1.006)
ax_zoom.set_xlabel("Orbital Phase", fontsize=10, color=INK)
ax_zoom.tick_params(axis="both", labelsize=8, colors=INK_SOFT, length=0)
ax_zoom.tick_params(axis="y", labelleft=False)
ax_zoom.xaxis.set_major_formatter(FormatStrFormatter("%.2f"))
ax_zoom.spines["top"].set_visible(False)
ax_zoom.spines["right"].set_visible(False)
for s in ("left", "bottom"):
ax_zoom.spines[s].set_color(INK_SOFT)
ax_zoom.yaxis.grid(True, alpha=0.15, linewidth=0.6, color=INK)
ax_zoom.set_title("Transit Detail", fontsize=10, fontweight="medium", pad=8, color=INK)
# Figure title — "lightcurve-transit · python · matplotlib · anyplot.ai" is ~53 chars, fits at 12pt
fig.suptitle(
"lightcurve-transit · python · matplotlib · anyplot.ai", fontsize=12, fontweight="medium", y=0.98, color=INK
)
fig.subplots_adjust(left=0.09, right=0.97, top=0.91, bottom=0.12, wspace=0.15)
plt.savefig(f"plot-{THEME}.png", dpi=400, facecolor=PAGE_BG)
Part of Astronomical Light Curve on anyplot.ai.